Field of the Invention
This invention relates generally to an arrangement of antennas in a vehicle and, more particularly, to an arrangement of multiple-input multiple-output (MIMO) antennas that provide 4G mobile communications services within a vehicle, such as an automobile.
Discussion of the Related Art
The current state of the art for mobile cellular wireless communications technology is known as 4G, which provides a greater data throughput and bandwidth than previous cellular communications technologies, such as 2G and 3G. The 4G cellular technology employs MIMO antennas at the transmitter and the receiver that provide an increase in the number of signal paths between the transmitter and the receiver, including multipath reflections off of various objects between the transmitter and the receiver, which allows for the greater data throughput. As long as the receiver can decouple the data being received on each path at the MIMO antennas where the signals are uncorrelated, then those paths can be used by the receiver to decipher data transmitted at the same frequency and at the same time. Thus, more data can be compressed into the same frequency providing higher bandwidth.
Modern vehicles employ various and many types of antennas to receive and transmit signals for different communications systems, such as terrestrial radio (AM/FM), cellular telephone, satellite radio, dedicated short range communications (DSRC), GPS, etc. Often the antennas used for these systems are integrated in a common antenna structure that is mounted to a roof of the vehicle so as to provide maximum reception capabilities.
Automobile manufacturers are looking to provide 4G cellular technology in vehicles, which presents a number of design challenges especially if the MIMO antennas are incorporated as part of the common antenna structure mounted to the roof of the vehicle. For example, by housing the MIMO antennas, which include at least two antennas, in the traditional telematics antenna module mounted to the roof of the vehicle, the entire antenna volume of the module would need to increase because of the extra real estate required for the MIMO antennas, which require a low correlation of the received signals at the antennas. In other words, because the signals received by the MIMO antennas need to be significantly uncorrelated, the distance between the antennas needs to be some minimum distance depending on the frequency band employed. Due to the increased size and volume of the antenna module, the required packaging for the MIMO antennas may no longer meet the styling and other requirements of the vehicle.